Rear subframe structure

ABSTRACT

A rear subframe structure is provided with a rear subframe including a front cross member, and a pair of left and right side members connected to the front cross member, and further including a vehicle-body mounting portion formed on both ends of the front cross member. The rear subframe includes a tunnel portion formed in a middle of a lower portion of the front cross member, and a brace extending in the vehicle width direction, and including a tunnel-portion mounting portion on left and right ends thereof. The brace includes a middle downwardly bulging portion bulging downwardly, and an upwardly bulging portion continued outwardly of the middle downwardly bulging portion and bulging upwardly. An inflection point between the middle downwardly bulging portion and the upwardly bulging portion is substantially located on an imaginary line linearly connecting the left and right tunnel-portion mounting portions in the vehicle width direction.

TECHNICAL FIELD

The present invention relates to a rear subframe structure of a vehicle,and more particularly, to a rear subframe structure provided with a rearsubframe including a front cross member extending in a vehicle widthdirection, and a pair of left and right side members connected to thefront cross member and extending in a vehicle front-rear direction; anda vehicle-body mounting portion formed on both ends of the front crossmember in the vehicle width direction.

BACKGROUND ART

Generally, a rear subframe is configured such that a pair of front andrear cross members extending in a vehicle width direction, and left andright side members extending in a vehicle front-rear direction areconnected substantially in a grid pattern in a plan view of a vehicle.

In a case where the aforementioned rear subframe is mounted on a vehicleconfigured such that the height of a rear seat pan is set low in orderto secure comfort of a passenger seated on a rear seat and to secure alow hip point, a portion above a front-side vehicle-body mountingportion of the rear subframe is restricted by the rear seat pan.Furthermore, it is necessary to dispose a propeller shaft and an exhaustpipe in the vehicle front-rear direction. Therefore, a front crossmember constituting the rear subframe may be formed into a saddle shape.

In order to reinforce a lower portion of the saddle-shaped front crossmember, it is proposed to dispose a brace below the saddle-shapedportion in the vehicle width direction. However, there is a problem thatit is difficult to dispose a thick brace in a straight manner in thevehicle width direction in a case where an exhaust pipe and a propellershaft are disposed in a narrow space restricted by the rear seat pan.

Patent Literature 1 discloses a configuration, in which an upper memberelement corresponding to a rear subframe is provided, a saddle-shapedportion for receiving a propeller shaft in a vehicle front-reardirection is formed on the upper member element, and a lower memberelement corresponding to a brace is provided below the saddle-shapedmember.

However, in the conventional structure disclosed in Patent Literature 1,in view of a point that the aforementioned lower member element isformed substantially linearly in the vehicle width direction in a frontview, there is a problem that the layout of an exhaust pipe isdeteriorated in a case where the aforementioned conventional structureis employed in a vehicle configured such that the height of a rear seatpan is set low. Thus, there is room for improvement.

CITATION LIST Patent Literature

Patent Literature 1: U.S. Pat. No. 5,833,026

SUMMARY OF INVENTION

In view of the above, an object of the present invention is to provide arear subframe structure which enables to secure a substantially linearload transmission path in a vehicle width direction while avoiding apropeller shaft and an exhaust pipe, and to reinforce a front crossmember even in a portion where it is difficult to dispose a thick bracein a straight manner in the vehicle width direction.

An aspect of the present invention is directed to a rear subframestructure provided with a rear subframe including a front cross memberextending in a vehicle width direction, and a pair of left and rightside members connected to the front cross member and extending in avehicle front-rear direction; a vehicle-body mounting portion formed onboth ends of the front cross member in the vehicle width direction; atunnel portion formed in a middle of a lower portion of the front crossmember through which a propeller shaft extends; and a brace extending inthe vehicle width direction below the tunnel portion, and including atunnel-portion mounting portion on left and right ends thereof. Thebrace includes a middle downwardly bulging portion bulging downwardlywhile avoiding the propeller shaft, and an upwardly bulging portioncontinued outwardly of the middle downwardly bulging portion in thevehicle width direction and bulging upwardly while avoiding an exhaustpipe. An inflection point between the middle downwardly bulging portionand the upwardly bulging portion is substantially located on animaginary line linearly connecting the left and right tunnel-portionmounting portions in the vehicle width direction.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a rear subframe structure according tothe present invention;

FIG. 2 is a plan view of the rear subframe structure;

FIG. 3 is a bottom view of the rear subframe structure;

FIG. 4 is a front view of the rear subframe structure;

FIG. 5 is a rear view of the rear subframe structure;

FIG. 6 is a perspective view of the rear subframe structure when viewedfrom rear on a vehicle left side;

FIG. 7 is a perspective view of the rear subframe structure when viewedfrom rear and above on a vehicle right side;

FIG. 8A is a sectional view taken along the line A-A in FIG. 2;

FIG. 8B is a sectional view taken alone the line B-B in FIG. 2;

FIG. 9 is a sectional view taken along the line C-C in FIG. 2;

FIG. 10 is a side view illustrating essential parts of FIG. 2;

FIG. 11 is a sectional view taken along the line D-D in FIG. 10;

FIG. 12A is a plan view of a partition member;

FIG. 12B is a perspective view of the partition member;

FIG. 13A is a perspective view of a stabilizer support member; and

FIG. 13B is a front view of a brace.

DESCRIPTION OF EMBODIMENTS

In the following, an embodiment of the present invention is described indetail based on the drawings.

FIG. 1 is a perspective view of a rear subframe structure, FIG. 2 is aplan view of the rear subframe structure, FIG. 3 is a bottom view of therear subframe structure, FIG. 4 is a front view of the rear subframestructure, and FIG. 5 is a rear view of the rear subframe structure. InFIG. 1, the arrow F indicates a vehicle front side, the arrow Rindicates a vehicle rear side, the arrow IN indicates an inner side in avehicle width direction, and the arrow OUT indicates an outer side in avehicle width direction (the same definition is also applied to theother drawings).

Referring to FIG. 1 to FIG. 5, a rear subframe 10 for supporting a rearsuspension includes a front cross member 11 extending in the vehiclewidth direction on the front side, a rear cross member 12 extending inthe vehicle width direction on the rear side of the front cross member11, a pair of upper side members 13 and 13 for connecting the frontcross member 11 and the rear cross member 12 in a vehicle front-reardirection, and a pair of lower side members 14 and 14 for connecting thefront cross member 11 and the rear cross member 12 in the vehiclefront-rear direction. These members are connected substantially in agrid pattern in a plan view of a vehicle. Each of the members 11 to 14has a closed sectional structure.

In the embodiment, the upper side member 13 is connected to a lateralportion of the front cross member 11 in the vehicle width direction viaa pillar portion 33 (see FIG. 10) to be described later, and extendsfrom the connection portion rearwardly of a vehicle.

Further, the rear cross member 12 connects rear portions of the pairedleft and right upper side members 13 and 13 in the vehicle widthdirection, connects rear portions of the paired left and right lowerside members 14 and 14 in the vehicle width direction, and furtherconnects the upper and lower side members 13 and 14 in an up-downdirection.

As illustrated in FIG. 2, the lower side member 14 is located on theinner side than the upper side member 13 in the vehicle width direction,and connects a lower portion of the front cross member 11 and a lowerportion of the rear cross member 12 in the vehicle front-rear direction.

As illustrated in FIG. 2 and FIG. 3, a distance between rear ends of thepaired left and right lower side members 14 and 14 is set smaller than adistance between front ends of the paired left and right lower sidemembers 14 and 14. Thereby, lower-arm rear-side support portions 12 band 12 c (see FIG. 6) to be described later are formed at positionswhere the lower-arm rear-side support portions 12 b and 12 c overlap theupper side member 13 in a plan view.

As illustrated in FIG. 1 to FIG. 5, front-side vehicle-body mountingportions 15 and 15 are formed on both ends of the front cross member 11in the vehicle width direction. A rear portion of the upper side member13 is smoothly formed into a curve rearwardly of the vehicle andoutwardly in the vehicle width direction. Rear-side vehicle-bodymounting portions 16 and 16 are formed on rear ends of the upper sidemembers 13 and 13. The rear subframe 10 is mounted to a vehicle body,specifically, to a rear side frame via the vehicle-body mountingportions 15 and 16.

The reference numeral 17 denotes a lower arm. A link support portion 17a is formed on a front portion of an outer end of the lower arm 17 inthe vehicle width direction. A lower end of an integral link 18 ispivotally supported on the link support portion 17 a. An upper end ofthe integral link 18 is pivotally connected to an integral link supportportion of a hub support 19.

The integral link 18 is a link for controlling a recession angle (anangle defined by a road surface, and a swing trajectory of a rear wheelin a side view when the rear wheel moves up and down in a case where therear wheel rides on a step).

In the embodiment, an H-shaped lower arm is employed as the lower arm17. A connection portion 17 b is formed on a rear portion of an outerend of the lower arm 17 in the vehicle width direction (see FIG. 3). Theconnection portion 17 b is pivotally connected to a lower-arm supportportion of the hub support 19.

The reference numeral 20 denotes a toe control link for setting a rearwheel to toe-in so as to secure wheel straightness. A connection portion20 a is formed on an outer end of the toe control link 20 in the vehiclewidth direction. The connection portion 20 a is pivotally connected to atoe control link support portion of the hub support 19.

The reference numeral 21 denotes an upper arm. A connection portion 21 ais formed on an outer end of the upper arm 21 in the vehicle widthdirection. The connection portion 20 a is pivotally connected to anupper-arm support portion of the hub support 19. In the embodiment, anI-shaped upper arm is employed as the upper arm 21.

As illustrated in FIG. 1, FIG. 4, and FIG. 5, a damper support portion19 a extending inwardly in the vehicle width direction is integrallyformed on the hub support 19. A damper 22 of a strut structure ismounted on the damper support portion 19 a.

As illustrated in FIG. 2 and FIG. 3, a bulging portion 17 c bulgingrearwardly is formed on a rear portion of the lower arm 17. A coilspring 24 is wound between a spring lower retainer 23 mounted on anupper portion of the bulging portion 17 c, and a spring upper retainer(not illustrated) provided on the rear side frame on the vehicle bodyside.

As illustrated in FIG. 2, FIG. 3, and FIG. 5, a stabilizer 25 isprovided on the rear side of the rear cross member 12 along the rearcross member 12. The stabilizer 25 is formed into a bent shape forwardlyof a vehicle in such a manner that left and right ends of the stabilizer25 are located above the lower arm 17. The bent ends of the stabilizer25 are connected to the lower arm 17 by using a connection member. Thestabilizer 25 is configured to suppress a roll angle when one wheel isbumped or rebound by torsional rigidity resistance.

As illustrated in FIG. 4, a tunnel portion 11 a for receiving apropeller shaft 26 in the vehicle front-rear direction is formed in themiddle of a lower portion of the front cross member 11. The front crossmember 11 is formed into a saddle shape. Further, a brace 27 as areinforcement member for connecting lower portions of the tunnelportions 11 a in the vehicle width direction is provided.

As illustrated in FIG. 1 to FIG. 3, a differential mount portion 12 a isformed on an intermediate portion of the rear cross member 12 in thevehicle width direction. A differential mount bracket 29 is mounted onthe differential mount portion 12 a via a differential mount bush 28.

A vehicle in the embodiment is a vehicle of a type such that a drivingforce is transmitted to rear wheels. The vehicle is configured such thata rear portion of a rear differential device (not illustrated) issupported by the differential mount bracket 29.

FIG. 6 is a perspective view of the rear subframe structure when viewedfrom rear on a vehicle left side, FIG. 7 is a perspective view of therear subframe structure when viewed from rear and above on a vehicleright side, FIG. 8A is a sectional view taken along the line A-A in FIG.2, FIG. 8B is a sectional view taken along the line B-B in FIG. 2, FIG.9 is a sectional view taken along the line C-C in FIG. 2, FIG. 10 is aside view illustrating essential parts of FIG. 2, and FIG. 11 is asectional view taken along the line D-D in FIG. 10.

FIG. 6 to FIG. 11 illustrate a configuration of a vehicle left sideportion. The configuration of a vehicle right side portion issymmetrical or substantially symmetrical with respect to theconfiguration of the vehicle left side portion in a left-rightdirection.

As illustrated in FIG. 8A, FIG. 8B, FIG. 9, and FIG. 11, the front crossmember 11 has a structure such that a front panel 31 located on thefront side and a rear panel 32 located on the rear side are joined andfixed, and has a closed section S1 extending in the vehicle widthdirection. Specifically, the closed section S1 is constituted by therear panel 32 on the middle side (specifically, on the rear side) of therear subframe 10, and the front panel 31 including an upper surface 31 aextending rearwardly than the rear panel 32 and including a frontsurface 31 b extending downwardly than the rear panel 32.

As illustrated in FIG. 1 and FIG. 6, left and right lateral portions ofthe front cross member 11 are inclined outwardly in the vehicle widthdirection, and forwardly and downwardly. Thereby, as illustrated in FIG.8B and FIG. 9, a front portion of the closed section S1 extendsdownwardly to form an enlarged closed section S1 a. Further, asillustrated in FIG. 8B and FIG. 9, a rear portion of the closed sectionS1 on a lateral portion of the front cross member 11 in the vehiclewidth direction is projected upwardly and forwardly to form a recessedclosed section S1 b. The enlarged closed section S1 a and the recessedclosed section S1 b are continued.

As illustrated in FIG. 6, FIG. 8B, and FIG. 9, there is formed, on arear portion of the enlarged closed section S1 a, a lower-arm supportportion 32 a for supporting a front mounting portion 17 d out of frontand rear mounting portions 17 d and 17 e of the lower arm 17.

As illustrated in FIG. 8B, the upper side member 13 is connected to arear surface of an upper portion of the closed section S1, specifically,to a rear surface of the recessed closed section S1 b via the pillarportion 33.

As described above, by inclining a lateral portion of the front crossmember 11 in the vehicle width direction forwardly and downwardly, it ispossible to enlarge a front portion of the closed section S1 downwardly(see the enlarged closed section S1 a), while avoiding interference witha rear seat pan (a rear floor panel), whereby rigidity in the vehiclewidth direction is secured without narrowing a swing range of the lowerarm 17.

In other words, even in a structure configured such that the rearsubframe 10 is disposed in a narrow space of a lower portion of a rearseat pan where it is not possible to connect the front cross member 11and the upper side member 13, while securing a sufficient closedsectional structure (a linearly extending closed sectional structure),it is possible to secure high rigidity in the vehicle width direction,and to secure a space for the lower-arm support portion 32 a(specifically, secure a space for the mounting portion 17 d of the lowerarm 17).

As illustrated in FIG. 6, FIG. 7, and FIG. 8B, the pillar portion 33 hasa shape of a closed section S2 constituted by a rear plate 34 includingan upper-arm support portion 34 a for supporting a mounting portion 21 b(see FIG. 2) of the upper arm 21, and a front plate 35 including alower-arm support portion 35 a. As illustrated in FIG. 6 and FIG. 11,the rear plate 34 is formed to have a U-shaped section in a plan view.

As illustrated in FIG. 7, the front plate 35 includes a dome-shapedflange portion 35 b which extends from an outer peripheral edge of amain surface portion thereof forwardly of the vehicle, and which isabutted against a back surface of the rear panel 32 of the front crossmember 11 and welded.

As illustrated in FIG. 8B and FIG. 9, a second closed section S3extending in the vehicle width direction is constituted by the closedsection S1 of a lateral portion of the front cross member 11 in thevehicle width direction, the front plate 35 located immediately on therear side of the closed section 51, and an upper surface of the lowerside member 14. Thereby, a space for supporting a lower arm is secured,and connection rigidity of the lower side member 14 is enhanced.

As illustrated in FIG. 7, a lower portion of the front plate 35 is fixedby abutment against an upper surface of the lower side member 14 andagainst an outer lateral surface of the lower side member 14 in thevehicle width direction and by welding.

As illustrated in FIG. 8B, the pillar portion 33 having a structure ofthe closed section S2 is formed immediately on the rear side of thesecond closed section S3. The pillar portion 33 includes the front plate35, extends upwardly from the lower side member 14, and is connected toa back surface of the front cross member 11. A rear surface of an upperportion of the pillar portion 33, specifically, a rear surface of anupper portion of the rear plate 34 is connected to a front portion ofthe upper side member 13 by welding.

In other words, the front-side lower-arm support portion 32 a out of thelower-arm support portions 32 a and 35 a is formed by a part (a part ofthe enlarged closed section S1 a) configured such that a front portionof the closed section S1 extends downwardly out of a lateral portion ofthe front cross member 11 in the vehicle width direction, and therear-side lower-arm support portion 35 a is formed by the pillar portion33 having a structure of the closed section S2. Further, the pillarportion 33 is connected to all of the upper side member 13, the lowerside member 14, and the front cross member 11. According to thisconfiguration, it is possible to distribute load to be input via thelower-arm support portions 32 a and 35 a, and to attain high rigidity ofthe rear subframe 10.

Further, in order to secure a sufficient space for supporting a lowerarm while lowering a lateral portion of the front cross member 11 in thevehicle width direction, the pillar portion 33 (specifically, the rearplate 34) is used as a set plate, while reducing the size of therecessed closed section S1 b in the up-down direction than the size ofthe upper side member 13 in the up-down direction, whereby connectionrigidity is enhanced.

As illustrated in FIG. 6, FIG. 7, and FIG. 8B, the vertical-wall-shapedpillar portion 33 constituted by the front plate 35 and the rear plate34, and extending in the vehicle width direction and in the up-downdirection is held and fixed between a lateral portion of the front crossmember 11 in the vehicle width direction, and a front end of the upperside member 13.

As illustrated in FIG. 6, FIG. 7, and FIG. 8B, a lower portion of thepillar portion 33, specifically, lower portions of the front plate 35and the rear plate 34 are respectively connected to an upper surface ofthe lower side member 14 and to an outer lateral surface of the lowerside member 14 in the vehicle width direction. The upper-arm supportportion 34 a is formed on an upper portion of the rear plate 34, and thelower-arm support portion 35 a is formed on a lower portion of the frontplate 35.

According to the aforementioned configuration, load input from the upperand lower arms (the lower arm 17 and the upper arm 21) is directlytransmitted to the upper and lower side members 13 and 14 and to thefront cross member 11 for load distribution, whereby high rigidity ofthe rear subframe 10 is attained. Further, the upper and lower armsupport portions 34 a and 35 a are formed on the pillar portion 33. Thismakes it possible to enhance positioning accuracy between the lower arm17 and the upper arm 21.

As illustrated in FIG. 6, FIG. 7, and FIG. 10, the upper-arm supportportion 34 a includes a substantially Z-shaped upper-arm support bracket36 on a rear portion thereof in a side view.

The upper-arm support bracket 36 includes a vertical piece 36 aextending in the up-down direction, an upper piece 36 b extendingrearwardly from an upper end of the vertical piece 36 a, and a lowerpiece 36 c extending forwardly from a lower end of the vertical piece 36a. The upper-arm support bracket 36 is integrally formed by these pieces36 a to 36 c. As illustrated in FIG. 10, an upper half of the verticalpiece 36 a and the upper piece 36 b are abutted against an outer lateralsurface of the upper side member 13 in the vehicle width direction andwelded, and a front end of the lower piece 36 c is abutted against aback surface of the rear plate 34 and welded.

As illustrated in FIG. 10, the upper-arm support bracket 36 holds thepillar portion 33 in cooperation with the front cross member 11.Further, a front portion of the upper side member 13 and the pillarportion 33 are connected by the upper-arm support bracket 36. By theaforementioned holding structure of the pillar portion 33 by theupper-arm support bracket 36 and the front cross member 11, the pillarportion 33 is securely supported, and the upper arm 21 is supported bythe upper-arm support portion 34 a on the upper portion of the pillarportion 33 and the upper-arm support bracket 36, whereby supportrigidity of the upper arm 21 is enhanced. Further, connection rigiditybetween the pillar portion 33 and the upper side member 13 is enhanced.

As illustrated in FIG. 8B, an upper portion of the rear plate 34 of thepillar portion 33 is directly connected to the front cross member 11(specifically, a rear portion of the upper surface 31 a of the frontpanel 31), and the lower-arm support portions 35 a and 32 a areconstituted by a lower portion of the front plate 35 and a lower portionof the front cross member 11 (specifically, a lower portion of the rearpanel 32). Thus, load from the upper arm 21 and the lower arm 17 istransmitted to the front cross member 11 and to the upper and lower sidemembers 13 and 14 for load distribution, and high rigidity of the rearsubframe 10 is attained.

As illustrated in FIG. 8B and FIG. 10, the pillar portion 33 extends inthe up-down direction between the upper side member 13 and the lowerside member 14, and the lower-arm support portion 35 a is formed on afront surface of the pillar portion 33 on an upper side of the lowerside member 14, in other words, on the front plate 35.

Further, as illustrated in FIG. 6, FIG. 7, and FIG. 8B, a toe controllink support portion 34 b is formed on a rear surface of the pillarportion 33 located below the lower-arm support portion 35 a, and on anouter lateral side of the lower side member 14 in the vehicle widthdirection, in other words, on the rear plate 34.

As illustrated in FIG. 6, FIG. 7, and FIG. 11, a toe control linksupport bracket 37 (hereinafter, simply referred to as a link supportbracket) for supporting the toe control link support portion 34 b fromthe rear side is provided on the rear subframe 10.

As illustrated in FIG. 6, FIG. 7, and FIG. 11, the link support bracket37 includes a front piece 37 a fixed upright on an upper surface of thelower side member 14 and extending in the vehicle front-rear direction,and a lateral piece 37 c extending from a rear end of the front piece 37a outwardly in the vehicle width direction. The link support bracket 37is integrally formed by these pieces 37 a and 37 b. A horizontallyU-shaped cutaway portion 37 b is formed in the lateral piece 37 c. Thecutaway portion 37 b of the lateral piece 37 c is welded and fixed to anupper surface, an outer lateral surface, and a lower surface of thelower side member 14.

Further, the link support bracket 37 is mounted between the lower sidemember 14 and a back surface of the lower-arm support portion 35 a ofthe pillar portion 33.

The lower-arm support portion 35 a and the toe control link supportportion 34 b are displaced in the up-down direction. Thereby, a compactand dense layout by the support portions 35 a and 34 b, the lower arm17, and the toe control link 20 is obtained. Further, load from thelower arm 17 and the toe control link 20 is distributed to an uppersurface and a lateral surface of the lower side member 14, and furtherto the upper and lower side members 13 and 14, whereby high rigidity ofthe rear subframe 10 is attained. In addition to the above, the pillarportion 33 supports two components i.e. the lower arm 17 and the toecontrol link 20 to enhance positioning accuracy between the lower arm 17and the toe control link 20.

The lower-arm support portion 35 a for supporting the lower arm 17 isformed as a first arm support portion. Therefore, it is possible tooffset the front mounting portion 17 d of the lower arm 17 to the innerside in the vehicle width direction than an outer lateral edge of thelower side member 14 in the vehicle width direction. Thus, it ispossible to enhance freedom in setting an imaginary lower-arm swingcenterline L illustrated in FIG. 8B.

As illustrated in FIG. 8B, the vehicle-body mounting portions 17 d and17 e are formed on front and rear portions of the lower arm 17 to besupported by the lower-arm support portion 35 a. Specifically, the lowerarm 17 includes the front mounting portion 17 d on the front side withrespect to the pivot center of the lower arm 17, and the rear mountingportion 17 e on the rear side with respect to the pivot center of thelower arm 17.

Further, the lower-arm rear-side support portions 12 b and 12 cconnected to the rear cross member 12 or integrally formed with the rearcross member 12 are formed such that the first swing centerline Llocated on the lower side than the lower-arm support portion 35 a of thepillar portion 33 and passing through the front and rear mountingportions 17 d and 17 e of the lower arm 17 is located on the upper sidethan the link support portion 34 b.

As illustrated in FIG. 8B, the upper and lower side members 13 and 14are connected by the rear cross member 12 in the up-down direction, andform a rigid box-shaped structure. Further, the rear-side supportportions 12 b and 12 c of the lower arm 17 are formed on a lower portionof the rear cross member 12 to distribute load of the lower arm 17 inthe front-rear direction via the front and rear mounting portions 17 dand 17 e. Further, the lower-arm swing centerline L (an imaginary axis)is formed on the upper side than the link support portion 34 b with anangle at which the front and rear mounting portions 17 d and 17 e of thelower arm 17 obtain a recession angle. Thereby, even in a narrow spacesuch that the rear seat pan comes close, it is possible to rigidly formthe lower-arm front-side support portion 35 a and the link supportportion 34 b.

Specifically, it is possible to avoid interference with the toe controllink 20, while enhancing support rigidity by a support portion of thelower arm 17, whereby it is easy to set a recession angle.

As illustrated in FIG. 9 and FIG. 10, the rear cross member 12 forconnecting the upper side member 13 and the lower side member 14 in theup-down direction has a structure of a closed section S4 of a T-shape ina side view, whose size is increased in the vehicle front-rear directionalong an inner lateral surface of the upper side member 13 in thevehicle width direction (in other words, an inner hollow structure of aT-shape in a side view).

As illustrated in FIG. 1 and FIG. 2, the closed section S4 of a T-shapein a side view is formed only on left and right side portions of therear cross member 12. As illustrated in FIG. 8A, a closed section S5extending in the up-down direction and having an I-shape in a side viewis formed on an intermediate portion of the rear cross member 12 in thevehicle width direction. The closed sections S4 and S5 communicate witheach other.

Further, as illustrated in FIG. 9, the lower-arm rear-side supportportions 12 b and 12 c are formed on the lower side of a lateral portionof the rear cross member 12 in the vehicle width direction, which isassociated with the closed section S4 of a T-shape in a side view; andthe rear mounting portion 17 e of the lower arm 17 is supported by thelower-arm rear-side support portions 12 b and 12 c.

The rear cross member 12 including the closed section S4 of a T-shape ina side view includes, on an upper portion thereof, an upper-surfacefront-side projection portion 12 d and an upper-surface rear-sideprojection portion 12 e bulging in the vehicle front-rear direction. Astabilizer support bracket 38 is mounted between the upper-surfacerear-side projection portion 12 e, and the rear-side lower-arm rear-sidesupport portion 12 c (in this embodiment, near the rear-side lower-armrear-side support portion 12 c) out of the paired front-side andrear-side lower-arm rear-side support portions 12 b and 12 c.

As described above, forming the rear cross member 12 into a structure ofthe closed section S4 of a T-shape in a side view makes it possible toincrease the size of a closed section of the rear cross member 12 and toenhance rigidity. Further, mounting the stabilizer support bracket 38between the upper-surface rear-side projection portion 12 e and thelower-arm support portion 12 c of the rear cross member 12 makes itpossible to reinforce the rear cross member 12 by the stabilizer supportbracket 38, and to secure a space for installing the stabilizer 25without increasing the number of parts.

FIG. 13A is a perspective view illustrating the stabilizer supportbracket 38. As illustrated in FIG. 13A, the stabilizer support bracket38 is integrally formed by a pair of inner and outer lateral pieces 38 aand 38 b in the vehicle width direction, and a rear piece 38 c forconnecting the lateral pieces 38 a and 38 b. The rear piece 38 c isinclined in a state that a front portion thereof is inclined downwardlyand a rear portion thereof is inclined upwardly when assembling thestabilizer support bracket 38 to the rear subframe 10 (specifically, therear cross member 12) is completed.

The stabilizer 25 is mounted to a back surface of the rear piece 38 c ofthe stabilizer support bracket 38 with use of a support bracket 39,which is fastened by a bolt and a nut (see FIG. 6 and FIG. 9).

As illustrated in FIG. 1 and FIG. 2, there are formed, on a top portionof the rear cross member 12, a ridge X1 extending in the vehicle widthdirection on an intermediate portion thereof in the vehicle widthdirection, ridges X2 and X2 extending outwardly in the vehicle widthdirection from left and right ends of the ridge X1 along an upper end ofa front portion of the upper-surface front-side projection portion 12 d,and ridges X3 and X3 extending outwardly in the vehicle width directionfrom connection portions of the ridges X1 and X2 along an upper end of arear portion of the upper-surface rear-side projection portion 12 e. Theridges X1, X2, and X3 are combined substantially in an X-shape in a planview. Thereby, torsional rigidity of the rear cross member 12 isenhanced.

As illustrated in FIG. 9 and FIG. 10, a partition member 40 is providedwithin the closed section S4 in the vicinity of a lower end of thestabilizer support bracket 38 of the rear cross member 12. Alower-portion closed section S6 extending in the vehicle width directionis formed by the partition member 40 and an upper surface of the lowerside member 14.

Forming the lower-portion closed section S6 makes it possible to enhancelocal rigidity of the rear cross member 12 in the vehicle widthdirection, to increase load transmission from the lower-arm rear-sidesupport portions 12 b and 12 c, to prevent sectional deformation byconcentration of stress, and to enhance rigidity in the vehicle widthdirection.

FIG. 12A is a plan view of the partition member 40, and FIG. 12B is aperspective view of the partition member 40. The partition member 40includes a lower piece 40 a located within the closed section S4 of therear cross member 12 and extending in the vehicle width direction, and alateral piece 40 b extending from an outer end of the lower piece 40 ain the vehicle width direction upwardly by a predetermined amountcorresponding to a width of the rear cross member 12 in the front-reardirection, and then, whose sizes of front and rear portions areincreased. The partition member 40 is integrally formed by these pieces40 a and 40 b. As illustrated in FIG. 11, the lower piece 40 a is weldedand fixed to front and rear walls of the rear cross member 12. Asillustrated in FIG. 9, an upper end of the lateral piece 40 b is weldedand fixed to a lower surface of the upper-surface front-side projectionportion 12 d and to a lower surface of the upper-surface rear-sideprojection portion 12 e. The rear cross member 12 may be formed bycombining two members, or may be formed by a hydroformed component.

FIG. 13B is a front view enlargedly illustrating the brace 27. Asillustrated in FIG. 4 and FIG. 13B, the brace 27 includes a middledownwardly bulging portion 27 a bulging downwardly while avoiding thepropeller shaft 26, and a pair of left and right upwardly bulgingportions 27 b and 27 b bulging upwardly on left and right outer sides ofthe middle downwardly bulging portion 27 a in the vehicle widthdirection while avoiding an exhaust pipe 41 (the exhaust pipe 41 isprovided only on the vehicle right side). The brace 27 is integrallyformed by these portions. In this embodiment, the brace 27 isconstituted by an aluminum die cast member.

As illustrated in FIG. 13B, the middle downwardly bulging portion 27 a,and the upwardly bulging portions 27 b and 27 b on the left and rightsides of the middle downwardly bulging portion 27 a are smoothly andintegrally connected.

As illustrated in FIG. 3, tunnel-portion mounting portions 27 c and 27 c(hereinafter, simply referred to as mounting portions) extendingrearwardly up to the positions of the vehicle-body mounting portions ofthe toe control link 20 are integrally formed on lateral portions of thebrace 27 in the vehicle width direction.

Further, the brace 27 is formed in such a manner that an inflectionpoint between the middle downwardly bulging portion 27 a and theupwardly bulging portion 27 b is substantially located on an imaginaryline linearly connecting the left and right tunnel-portion mountingportions 27 c and 27 c in the vehicle width direction. According to thisconfiguration, as illustrated in FIG. 13B, a load transmission path 50for substantially linearly connecting the left and right mountingportions 27 c and 27 c in the vehicle width direction is formed in thebrace 27.

Specifically, preferably, an edge of a bulging portion on thenon-bulging side may be proximate to an imaginary line passing thoughthe left and right mounting portions 27 c and 27 c as illustrated inFIG. 13B, and more preferably, the edge may overlap the imaginary line.

Further, in a case where the edge is proximate to the imaginary linewithout overlapping, preferably, the bending amount of the edge on thenon-bulging side with respect to the imaginary line may be smaller thanthe bending amount of the edge on the bulging side, specifically, thedistance of the edge on the non-bulging side from the imaginary line maybe small, and the edge on the non-bulging side may have a shapeapproximate to a straight line.

According to the aforementioned configuration, even in a portion whereit is difficult to dispose a thick brace in a straight manner in thevehicle width direction, it is possible to secure the load transmissionpath 50 for linearly connecting the left and right mounting portions 27c and 27 c of the brace 27 in the vehicle width direction, whileavoiding the propeller shaft 26 and the exhaust pipe 41, and toreinforce the brace 27 itself by the bulging portions 27 a and 27 b tothereby reinforce the front cross member 11.

As illustrated in FIG. 4 and FIG. 13B, a differential mount portion 27 dfor supporting a differential mount bush 42 is provided for each of thepaired left and right upwardly bulging portions 27 b of the brace 27.This enables to reinforce the differential mount portion 27 d by theupwardly bulging portion 27 b, and to support a rear differential device(not illustrated) without increasing the number of parts. Thus, it isnot necessary to additionally provide a differential mount bracket onthe front side of the rear differential device.

As illustrated in FIG. 2, a rear differential device (not illustrated)is supported by the differential mount bush 42, and by the rear-sidedifferential mount bracket 29 located on the rear side of thedifferential mount bush 42.

As illustrated in FIG. 3 and FIG. 8B, the brace 27 is connected to thelower side member 14 at a position where the brace 27 overlaps, in abottom view, the lower-arm support portions 32 a and 35 a constituted bya lower portion of the front cross member 11, and the pillar portion 33formed on the rear side of the lower portion of the front cross member11.

Specifically, the mounting portion 27 c of the brace 27 is connected andfixed to a bottom surface of the lower side member 14 so as to overlapthe lower-arm support portions 32 a and 35 a in a bottom view with useof a plurality of fastening members 43 and 43 such as bolts at aposition away from the mounting portion 27 c in the front-reardirection. Thus, the lower-arm support portions 32 a and 35 a arereinforced with use of the brace 27.

In FIG. 1 and FIG. 5, the reference numeral 44 denotes an openingportion for weight reduction. In FIG. 6 and FIG. 7, the referencenumeral 45 denotes an opening portion for use in mounting the mountingportion 17 d of the lower arm 17. In FIG. 8A, the reference numeral 46denotes an arc-shaped recess portion for avoiding interference with aspare tire pan.

As described above, the rear subframe structure of the embodiment is arear subframe structure provided with the rear subframe 10 including thefront cross member 11 extending in the vehicle width direction, and apair of left and right side members (see the upper side members 13 and13) connected to the front cross member 11 and extending in the vehiclefront-rear direction; the vehicle-body mounting portions 15 and 15formed on both ends of the front cross member 11 in the vehicle widthdirection; the tunnel portion 11 a formed in the middle of a lowerportion of the front cross member 11 through which the propeller shaft26 extends; and the brace 27 for connecting a lower portion of thetunnel portion 11 a in the vehicle width direction. The brace 27includes the middle downwardly bulging portion 27 a bulging downwardlywhile avoiding the propeller shaft 26, and the upwardly bulging portion27 b bulging upwardly on the outer side of the middle downwardly bulgingportion 27 a in the vehicle width direction while avoiding the exhaustpipe 41. The brace 27 includes the load transmission path 50 forsubstantially linearly connecting the left and right mounting portions27 c and 27 c in the vehicle width direction (see FIG. 1, FIG. 4, andFIG. 13B).

According to the aforementioned configuration, even in a portion whereit is difficult to dispose a thick brace in a straight manner in thevehicle width direction, it is possible to secure the load transmissionpath 50 for linearly connecting the left and right mounting portions 27c and 27 c of the brace 27 in the vehicle width direction, whileavoiding the propeller shaft 26 and the exhaust pipe 41, and toreinforce the brace 27 itself by the bulging portions 27 a and 27 b tothereby reinforce the front cross member 11.

In the embodiment of the present invention, the differential mountportion 27 d for supporting the differential mount bush 42 is formed onthe upwardly bulging portion 27 b (see FIG. 4 and FIG. 13B).

According to the aforementioned configuration, it is possible toreinforce the differential mount portion 27 d by the upwardly bulgingportion 27 b, and to support a rear differential device, withoutincreasing the number of parts. Further, it is not necessary toadditionally provide a differential mount bracket.

In the embodiment of the present invention, the rear subframe 10 furtherincludes the rear cross member 12 extending in the vehicle widthdirection on a rear side of the front cross member 11, and the lowerside member 14 extending in the vehicle front-rear direction on a lowerside of the side member (the upper side member 13). The brace 27 isconnected to the lower side member 14 at a position where the brace 27overlaps, in a bottom view, the lower-arm support portions 32 a and 35 aconstituted by the lower portion of the front cross member 11, and thepillar portion 33 formed on a rear side of the lower portion of thefront cross member 11 between an upper portion of the front cross member11 and the lower side member 14, or between the side member (in otherwords, the upper side member 13) and the lower side member 14 (see FIG.3 and FIG. 8B).

According to the aforementioned configuration, it is possible toreinforce the lower-arm support portions 32 a and 35 a themselves by thebrace 27.

The following is a summary of the present invention as described above.

A rear subframe structure according to the present invention is a rearsubframe structure provided with a rear subframe including a front crossmember extending in a vehicle width direction, and a pair of left andright side members connected to the front cross member and extending ina vehicle front-rear direction; a vehicle-body mounting portion formedon both ends of the front cross member in the vehicle width direction; atunnel portion formed in a middle of a lower portion of the front crossmember through which a propeller shaft extends; and a brace extending inthe vehicle width direction below the tunnel portion, and including atunnel-portion mounting portion on left and right ends thereof. Thebrace includes a middle downwardly bulging portion bulging downwardlywhile avoiding the propeller shaft, and an upwardly bulging portioncontinued outwardly of the middle downwardly bulging portion in thevehicle width direction and bulging upwardly while avoiding an exhaustpipe. An inflection point between the middle downwardly bulging portionand the upwardly bulging portion is substantially located on animaginary line linearly connecting the left and right tunnel-portionmounting portions in the vehicle width direction.

According to the aforementioned configuration, even in a portion whereit is difficult to dispose a thick brace in a straight manner in thevehicle width direction, it is possible to secure a load transmissionpath for substantially linearly connecting the left and righttunnel-portion mounting portions of the brace in the vehicle widthdirection, while avoiding the propeller shaft and the exhaust pipe, andto reinforce the brace itself by the bulging portions to therebyreinforce the front cross member.

In an aspect of the present invention, a differential mount portion forsupporting a differential mount bush may be formed on the upwardlybulging portion.

According to the aforementioned configuration, it is possible toreinforce the differential mount portion by the bulging portion, and tosupport a rear differential device without increasing the number ofparts. Further, it is not necessary to additionally provide adifferential mount bracket.

In an aspect of the present invention, when it is assumed that the sidemember is an upper side member, the rear subframe may further include arear cross member extending in the vehicle width direction on a rearside of the front cross member, and a lower side member extending in thevehicle front-rear direction on a lower side of the upper side member.The brace is connected to the lower side member at a position where thebrace overlaps, in a bottom view, a lower-arm support portionconstituted by the lower portion of the front cross member, and a pillarportion formed on a rear side of the lower portion of the front crossmember between an upper portion of the front cross member and the lowerside member, or between the upper side member and the lower side member.

According to the aforementioned configuration, it is possible toreinforce the lower-arm support portion itself by the brace.

INDUSTRIAL APPLICABILITY

As described above, the present invention is advantageously applied to arear subframe structure provided with a rear subframe including a frontcross member extending in the vehicle width direction, and a pair ofleft and right side members connected to the front cross member andextending in a vehicle front-rear direction; and a vehicle-body mountingportion formed on both ends of the front cross member in the vehiclewidth direction.

1. A rear subframe structure, comprising a rear subframe including afront cross member extending in a vehicle width direction, and a pair ofleft and right side members connected to the front cross member andextending in a vehicle front-rear direction; a vehicle-body mountingportion formed on both ends of the front cross member in the vehiclewidth direction; a tunnel portion formed in a middle of a lower portionof the front cross member through which a propeller shaft extends; and abrace extending in the vehicle width direction below the tunnel portion,and including a tunnel-portion mounting portion on left and right endsthereof, wherein the brace includes a middle downwardly bulging portionbulging downwardly while avoiding the propeller shaft, and an upwardlybulging portion continued outwardly of the middle downwardly bulgingportion in the vehicle width direction and bulging upwardly whileavoiding an exhaust pipe, and an inflection point between the middledownwardly bulging portion and the upwardly bulging portion issubstantially located on an imaginary line linearly connecting the leftand right tunnel-portion mounting portions in the vehicle widthdirection.
 2. The rear subframe structure according to claim 1, whereina differential mount portion for supporting a differential mount bush isformed on the upwardly bulging portion.
 3. The rear subframe structureaccording to claim 1, wherein when it is assumed that the side member isan upper side member, the rear subframe further includes a rear crossmember extending in the vehicle width direction on a rear side of thefront cross member, and a lower side member extending in the vehiclefront-rear direction on a lower side of the upper side member, and thebrace is connected to the lower side member at a position where thebrace overlaps, in a bottom view, a lower-arm support portionconstituted by the lower portion of the front cross member, and a pillarportion formed on a rear side of the lower portion of the front crossmember between an upper portion of the front cross member and the lowerside member, or between the upper side member and the lower side member.